1. Field of the Invention
The present invention relates to a method for driving a plasma display panel (hereinafter referred to as xe2x80x9cPDPxe2x80x9d) of a matrix display scheme.
2. Description of the Related Art
An AC (alternate current discharge) type PDP is well-known, as one type of the display panels using a matrix display scheme.
The AC type PDP comprises a plurality of column electrodes (address electrodes) and a plurality of row electrodes arranged perpendicular to the column electrodes and forming one scanning line per pair. Each of the row electrodes and column electrodes is covered with a dielectric layer to separate them from a discharge space. The PDP has a structure in which a discharge cell corresponding to one pixel is formed at an intersection of a pair of row electrodes and a column electrode.
Japanese Patent kokai No. 4-195087 discloses a method for performing a halftone display for the PDP, a so-called subfield method by which one field period is divided into N subfields, in each of which light is emitted for a time period corresponding to weighting of each bit digit of N-bit pixel data.
When the subfield method is used, assuming that supplied pixel data comprises six bits, one field period is divided into six subfields SF1, SF2, . . . , and SF6, and a light emitting operation is performed in each subfield. When the light emission in the six subfields has been performed once, 64-gradation display can be provided for one field of image.
Each subfield comprises a simultaneous reset step Rc, a pixel data writing step Wc, and a light emission sustaining step Ic. In the simultaneous reset step Rc, all discharge cells of the PDP are simultaneously discharged (reset discharge), so that wall charges are uniformly erased in all the discharge cells. In the next pixel data writing step Wc, a selective writing discharge in each discharge cell is produced in accordance with pixel data. At this time, in a discharge cell in which the writing discharge is performed, a wall charge is formed to be a xe2x80x9clight emitting cell.xe2x80x9d On the other hand, a discharge cell in which the writing discharge has not been performed remains without a wall charge, so that it becomes a xe2x80x9cnon-light emitting cell.xe2x80x9d In the light emission sustaining step Ic, only the light emitting cells are forced to continue a light emitting state for a duration corresponding to weighting of each subfield. In this way, the sustaining light emission is performed at a light emitting duration ratio of 1:2:4:8:16:32 in order in each subfield SF1-SF6.
However, the reset discharge performed for all the discharge cells in the simultaneous reset step Rc involves a relatively strong discharge, i.e., light emission with a high luminance level. Also, since light emission free from pixel data occurs due to the reset discharge, there is a problem that the contrast of an image is reduced. Also, the power consumption due to the light emission also constitutes the cause of preventing a reduction in power consumption of the PDP.
It is an object of the present invention to provide a method for driving a plasma display apparatus which has an improved contrast while reducing power consumption.
In accordance with one aspect, the present invention is characterized by a method for driving a plasma display panel on the basis of input pixel data of a field comprising a plurality of row electrodes formed in pairs corresponding to each of a plurality of display lines, a plurality of column electrodes arranged to cross said row electrodes, each of said column electrodes forming a discharge cell corresponding to one pixel at each intersection with a pair of said plurality of row electrodes, a row electrode driving circuit for generating a row electrode driving pulse for driving said plurality of row electrodes, and a column electrode driving circuit for generating a column electrode driving pulse for driving said plurality of column electrodes. The method comprises the steps of (a) performing a reset discharge for initializing all of said discharge cells in said field, and (b) dividing a display period in said field into a plurality of subfields to perform a gradation display, further comprising the step (c) of changing the number of reset discharges in said step (a) in accordance with luminance data in said input pixel data in a field preceding to said field, when said field is displayed.
In accordance with another aspect, the invention is characterized by a method for driving a plasma display panel on the basis of input pixel data of a field, said plasma display panel comprising a plurality of row electrodes formed in pairs corresponding to each of a plurality of display lines, a plurality of column electrodes arranged to cross said row electrodes, each of said column electrodes forming a discharge cell corresponding to one pixel at each intersection with a pair of said plurality of row electrodes, a row electrode driving circuit for generating a row electrode driving pulse for driving said plurality of row electrodes, and a column electrode driving circuit for generating a column electrode driving pulse for driving said plurality of column electrodes. The method comprises the steps of (d) dividing a display period of said field into a plurality of subfields to perform a gradation display, and (e) performing a reset discharge for initializing all of said discharge cells in each of said subfields, further comprising the step (f) of changing the number of said reset discharges in said step (e) in accordance with luminance data of input pixel data in a preceding field to said field, when said input pixel data is displayed.
In accordance with further aspect, the invention is characterized by a method for driving a plasma display panel on the basis of input pixel data of a field, said plasma display panel comprising a plurality of row electrodes formed in pairs corresponding to each of a plurality of display lines, a plurality of column electrodes arranged to cross said row electrodes, each of said column electrodes forming a discharge cell corresponding to one pixel at each intersection with a pair of said plurality of row electrodes, a row electrode driving circuit for generating a row electrode driving pulse for driving said plurality of row electrodes, and a column electrode driving circuit for generating a column electrode driving pulse for driving said plurality of column electrodes. The method comprises the steps of (g) dividing a display period of said field into a plurality of subfields to perform a gradation display to perform a gradation display, and (h) performing a reset discharge for initializing all of said discharge cells in a first subfield of said field, further comprising the step of (i) changing the number of said reset discharges in said step (h) in accordance with luminance data of input pixel data in a preceding field to said field when said input pixel data is displayed.
According to the present invention, when one field of input pixel data is displayed, the number of reset discharges for initializing all discharge cells in every field display period is changed in accordance with luminance data of one field of input pixel data of the previous field to this field, so that the contrast of a screen can be improved by suppressing light emission by a discharge which does not relate directly to a display.